The majority of commercial ink-jet inks are water-based. Thus, their constituents are generally water-soluble, as in the case with many dyes, or water dispersible, as in the case with pigments. Furthermore, ink-jet inks have low viscosity (typically 5 cps or less.
In addition to the typical color and general image fade issues that occur in many ink-jet ink systems, ink-jet prints have also been known for poor durability when exposed to water or high humidity. This results from the use of water-soluble and water dispersible colorants within the water-based ink. In response to this problem, latex polymers that are compatible with ink jet inks have been incorporated with the inks. The latex can consist of small micron or submicron hydrophobic polymeric particles of high molecular weight that are dispersed in the aqueous ink-jet ink. When printed as part of an ink-jet ink, a latex component of the ink can form a film on a media surface, entrapping and protecting the colorant within the hydrophobic print film.
However, such latex compositions can create problems with respect to pen reliability. Inks containing a latex component typically have a drop velocity decrease as the drop ejection frequency of the ink jet pen is increased beyond a certain value. The velocity reduction negatively impacts drop placement accuracy on the printed media within a moderate frequency range. At higher frequencies, the velocity reduction mechanism prevents drop ejection altogether, which can lead to agglomeration of the ink on the printer nozzle. In view of the foregoing, there remains a need in the art for latex particles that are thermal shear stable, and for inks that can be used in high speed ink jet printers that exhibit good drop placement accuracy on the print media and stable drop ejection at high drop frequencies.